Depth dependent optoelectronic properties of Cu(In,Ga)Se2 with lateral resolution in the micron/submicron scale from luminescence studies

Optoelectronic properties relevant for photovoltaics, such as band gap, spectral absorption, and splitting of quasi- Fermi levels of chalcopyrites Cu(In,Ga)Se2 have been analyzed by luminescence with lateral highly resolved methods, such as confocal photoluminescence (PL) (≤1 μm). In addition to the high lateral resolution we get access to depth profiles via different samples thicknesses provided by etching of standard samples. Amongst lateral fluctuations of band gap (up to few tens of meV), spectral absorption, and splitting of quasi-Fermi levels (Δ(EFn-EFp) ≈ (20-30) meV) we identify the increase in band gap corresponding to the rise in Ga content towards the rear contact; we also see by luminescence a substantial lateral fluctuation of the band gap which is interpreted as an according large lateral fluctuation of the extension of the Ga depth profile towards the front side. This observation agrees well with lateral variations of Δ(EFn-EFp) that cannot be consistently interpreted without sufficient spatial resolution.